This invention relates to a semiconductor device such as a diode, a transistor and an integrated circuit, and more particularly to a semiconductor device encapsulated in a package of plastic resinous material.
Some semiconductor devices of this type have L-shaped terminals of narrow width formed along the bottom and side surfaces of the package. They are generally referred to as leadless type semiconductor devices.
When a semiconductor device of this type is mounted on a circuit board such as a printed circuit board, it is customary to provisionally attach the semiconductor device to the circuit board with adhesive so that those portions of the terminals of the device which are on the bottom surface of the package contact the conductive layer of the circuit board. Then, the circuit board with the semiconductor device thereon is turned upside down so that the device hangs down from the board. Then, the board is dipped in a bath of molten solder so that those portions of the terminals which are on the side surface of the package (and which extend continuously to those portions of the terminals which are on the bottom surface of the package) are soldered to the conductive layer of the circuit board.
The synthetic resin usually used as the material of the package, however, has low wettability to solder. When the package, after its top surface is faced downward, is dipped into a bath of molten solder as previously mentioned, the top surface of the package is pressed against the solder and forced into contact with the solder by the surface tension of the solder. However, it often happens that the side surfaces of the package are not wetted with solder so that those portions of the terminals with small area which are on the side surface of the package cannot be soldered to the conductive layer of the circuit board. This is particularly true with small-sized packages having, for example, a width of 2 to 3 mm and a height of 1 to 2 mm.
Accordingly, the primary object of the invention is to provide a semiconductor device having a package of plastic resinous material in which the terminals formed along the side surface of the package are securely soldered to the conductive layer of a printed circuit board.
Another object of the invention is to provide a semiconductor device having terminals on the side surfaces of the package which are so shaped as to improve the incomplete contact between the terminals and solder caused by the low wettability to solder of the package made of synthetic resin.